Experimental studies have suggested that raising or lowering intraocular pressure (IOP) causes damage to axons in the lamina scleralis (LS) region of the monkey optic nerve head, probably by structural deformation. Similar injuries to axons could explain visual damage in several human eye diseases, especially glaucoma. This research is designed to clarify the mechanism of injury to tissues in the LS region in the monkey eye caused by increasing or decreasing IOP. Attention will be directed to the region of the LS carrying arcuate nerve fiber bundles arising in retinal areas equivalent to Bjerrum areas in man. The course of these nerve fiber bundles will be defined using localized retinal injections of tritiated amino acids to label rapid orthograde axoplasmic transport which will be analyzed by radioautographic techniques. The orthograde transport studies will be verified by the use of localized nerve head injections of horseradish peroxidase (HRP) and the demonstration of retrogradely labeled ganglion cells in the retinae. Combined orthograde and retrograde axoplasmic transport studies utilizing eye injections of tritiated amino acids and brain injections of HRP will be performed in monkey eyes with elevated or decreased IOP. Tissues will be processed in normal and pathologic eyes to permit serial sections at both light and electron microscopic levels. Direct tissue pressure measurements will be made at various levels of IOP to characterize the gradient of pressure change across the LS. Computer-assisted three-dimensional reconstructions of tissue components will be generated from both light and electron microscopic serial sections in selected areas of the LS. Quantitation of alterations in tissue components induced by changing IOP will be performed utilizing computerized data.